feat: Validate workspace specification before accessing parts of it

src/pyhf/workspace.py

@@ -300,14 +300,15 @@ def __init__(self, spec, validate: bool = True, **config_kwargs):
 
         """
         spec = copy.deepcopy(spec)
-        super().__init__(spec, channels=spec['channels'])
         self.schema = config_kwargs.pop('schema', 'workspace.json')
         self.version = config_kwargs.pop('version', spec.get('version', None))
 
         # run jsonschema validation of input specification against the (provided) schema
         if validate:
             log.info(f"Validating spec against schema: {self.schema}")
-            schema.validate(self, self.schema, version=self.version)
+            schema.validate(spec, self.schema, version=self.version)
+
+        super().__init__(spec, channels=spec['channels'])
 
         self.measurement_names = []
         for measurement in self.get('measurements', []):

tests/test_workspace.py

@@ -910,3 +910,11 @@ def test_workspace_without_validation(mocker, simplemodels_model_data):
 
     pyhf.Workspace(dict(ws), validate=False)
     assert pyhf.schema.validate.called is False
+
+
+def test_workspace_invalid_specification():
+    spec = {"channels": [{"name": "SR", "samples_wrong_name": []}]}
+    # Ensure that an invalid specifications gets caught as such
+    # before a KeyError: 'samples' could be reached.
+    with pytest.raises(pyhf.exceptions.InvalidSpecification):
+        pyhf.Workspace(spec)